Indianapolis native Peter Kassig, who converted to Islam and changed his name to Abdul-Rahman during his yearlong captivity by Islamic State militants, has been beheaded, U.S. officials confirmed Sunday.

He was 26.

The Islamic State group distributed a video via social media early Sunday to announce the execution of Kassig, a humanitarian worker and former U.S. Army Ranger captured last year in Syria.

Survivors include his parents, Ed and Paula Kassig, Indianapolis, who said Sunday they were "heartbroken" by the news and pledged to "work every day to keep his legacy alive as best we can."

Why didn't someone ask a terrorism expert about people who convert under torture? How genuine could that be considered?

To me, those questions remain relevant, even though Kassig's own parents describe his conversion as sincere.

Even after his death, Ed and Paula Kassig referred to their son's Muslim name:

"We are heartbroken to learn that our son, Abdul-Rahman Peter Kassig, has lost his life as a result of his love for the Syrian people and his desire to ease their suffering," they said in a prepared statement. "Our heart also goes out to the families of the Syrians who lost their lives, along with our son."

More from the Indianapolis story:

On Oct. 1, 2013, Kassig was captured during an aid mission to Deir Ezzour, Syria, when a convoy of militants overtook his ambulance. His parents learned through a friend that their son had been taken hostage but kept silent for more than a year at the insistence of his captors, who threatened to kill him if they went public.

They broke their silence on Oct. 3, 2014, when ISIS named Kassig the group's next beheading target. Over the following weeks, his parents lobbied publicly for his release, highlighting their son's humanitarian efforts and what they said was his genuine conversion to Islam.

When his fate became clear Sunday, they continued referring to him by his Muslim name.

"Fed by a strong desire to use his life to save the lives of others, Abdul-Rahman was drawn to the camps that are filled with displaced families and to understaffed hospitals inside Syria," they said. "We know he found his home amongst the Syrian people, and he hurt when they were hurting."

The Quran (4:92) teaches that Muslims must not kill other Muslims unless it is an accident.

The passage roughly translates as: 'Never is it for a believer to kill a believer except by mistake. And whoever kills a believer by mistake - then the freeing of a believing slave and a compensation payment presented to the deceased's family [is required] unless they give [up their right as] charity.'

It also says that if the killed Muslim was a prisoner of war, then the killer must release a believing slave.

Many have cited the passage as evidence that hostages like Kassig may convert to save their life.

But the Daily Mail quoted Kassig's parents as saying his journey toward Islam started before his captivity, according to friends.

That same story noted:

Nonetheless, an anti-terror expert told MailOnline that conversion - whether forced or not - would do nothing to help hostages save their own lives.

Dr Andreas Krieg, a King's College London professor, spoke from Iraq to say: 'Conversion in the case of IS [Islamic State] would not save the individual from death.

'IS does not differentiate between Muslims and non-Muslims, they differentiate between those following their ideological construct of Islam and those that do not.

'Only those that adhere to their ideology, which they call Islam, are being spared.

'In the case of Western hostages, or hostages with Western passports, neither will save them.

'The propaganda value of these beheadings is just too precious for them to spoil it on ideological considerateness.'

He added that it is possible a form of Stockholm syndrome - where hostages sympathize with their captors - could have spurred on Kassig's fascination with the faith.